1. Field of the Invention
The present invention relates to light source equipment which converts light outgoing from a light source such as a semiconductor laser to a light beam having a required distribution light intensity, and in particular it relates to light source equipment, an optical scanner and data reading apparatus for which it is necessary to provide a light beam whose beam diameter in its optical axis direction is unchanged.
2. Description of the Related Art
Recently, a bar code reader which is able to read bar code information has widely been used for commodity control, etc. It is requested that in a current handy type laser bar code reader such an optical system is employed in which the 1/e.sup.2 diameter of a light intensity distribution on the scanning surface is greater in a direction (subscanning direction) orthogonal to the main scanning direction that in a scanning direction (main scanning direction), and with little change in the beam diameter in the optical axis direction is a little. According to a laser bar code reader which satisfies such requirements, it is possible to read a bar code recorded with long lines in the subscanning direction in a wide range in the optical axis direction and also possible to attempt to decrease noise.
Semiconductor lasers which are cheap in cost are mostly used light source for bar code readers. However, it causes a problem in that the astigmatic interval and radiation expanding angle are different among the respective components of a semiconductor laser. Conventionally, some light source equipment in which the astigmatic interval and radiation expanding angle are corrected are disclosed in technical literature.
It is disclosed that the astigmatic interval is corrected by using a cylindrical lens in the U.S. Pat. Nos. 4,253,735, 5,081,639, etc., a prism in Japanese Laid-open Patent Publication No. 110,009 of 1994, and a scanning mirror having a refracting power in Japanese Laid-open Patent Publication No. 55,178 of 1996.
Furthermore, a technique for adjusting the radiation expanding angle of a laser by a single lens is disclosed by Japanese Laid-open Patent Publication Nos. 254,925 of 1986, 109,317 of 1989, and 305,615 of 1992.
However, in a method using a cylindrical lens and a prism, there are some problems wherein the number of components is increased to cause the production cost to also increase and therein lies the difficulty in downsizing. Furthermore, the processing of a scanning mirror with refracting power is difficult without increasing production costs.
Still furthermore, there were some conventional single lenses for adjusting the radiation angle, in which the change in the beam diameter in the optical axis direction could not be decreased since there was an objective of improving the optical utilization efficiency.